1. Field of the Invention
This invention relates to the preparation of dental matrix bands from composite dental resins and, more specifically, to a manual pressure molding device which may be used by a dentist in his office to prepare dental matrices in a variety of selected contours for use in restoring teeth to their approximate original shape.
2. Description of the Prior Art
The advantages possessed by composite dental resins over dental amalgam alloys in the restoration ("filling") of teeth have led to increasing acceptance of the former. These advantages include color matching and smoothness, and bondability.
A known and widely-used restoration procedure employing composite fillings involves the removal of decayed material from a tooth, wrapping a matrix band around the tooth to define the volume which will contain the composite restoration material, inserting a wedge between the outer surface of the band and the adjacent tooth, placing the composite restoration material in the void and curing it to hardness, usually by irradiation with a source of actinic light, then removing the matrix band and wedge.
It has been recognized that removal of the matrix band in an interproximal restoration carried out by the foregoing procedure often results in the formation of an undesirable "open contact", in which the filling of the restored tooth and the surface of the adjacent tooth do not abut, but present a gap between them.
A number of procedures and devices have been developed with a view to reducing the number of open contacts in dental restoration. With composite filling materials, a recent approach to the problem has been to employ non-removable matrices, made of the same composite material as the filling or of a similar material bondable to the restored tooth and composite filling. Unlike conventional, removable and non-bondable matrix bands made of stainless steel or Mylar (TM), the non-removable matrix band or a portion of it remains in place after the resin-based filling is cured.
An example of this approach (i.e. non-removable composite matrix) is disclosed in U.S. Pat. No. 4,778,385 (Herrin) directed to a matrix having a concave inner surface for adhesion to a posterior tooth in restoration, made of the same material as the composite restoration. However, being pre-formed, pre-shaped and non-flexible, these matrices must be supplied to the dentist in a variety of forms. A matrix of the appropriate size and contour to cover the proximal cavity and to prevent a gap between the restoration and the adjacent tooth is put firmly in place with the assistance of a subsequently-removed wedge. The requirement for an inventory of variously shaped matrices is costly and inconvenient.
U.S. Pat. No. 5,035,615 (Din) discloses the use of a flexible, rectangular matrix band of composite material to generate the outside of the tooth being restored. The band may be formed by mixing a conventional light-activated filler material with a conventional light-cured liquid resin, drawing the mixture into a film and finally curing the film of which the matrix band is made. The flexible composite matrix band so produced is held firmly against the tooth being restored, passively abutting an adjacent tooth. A bonding agent is applied to the surface of the prepared cavity in the tooth and to the matrix band. After curing of the bonding agent the cavity is filled with a composite resin which is then cured, followed by removal by the dentist of unbonded portions of the matrix band.
Although thin and flexible, the matrix band of Din has no contour to adjust well to the outer contoured surface of the restored tooth. Placement of a contoured matrix which closely matches the shape of the tooth surface, after treating the tooth surface with a bonding agent, seals the matrix to the tooth. As the matrix is already fully cured, it does not shrink during the curing cycle of the restorative material, avoiding the formation of any gap between the bottom edge of the prepared cavity and the final restoration.